CVE-2020-9897 in macOS
Summary
by MITRE • 10/28/2021
An out-of-bounds write was addressed with improved input validation. This issue is fixed in iOS 14.2 and iPadOS 14.2, macOS Big Sur 11.0.1. Processing a maliciously crafted PDF may lead to arbitrary code execution.
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Analysis
by VulDB Data Team • 11/01/2021
The vulnerability identified as CVE-2020-9897 represents a critical out-of-bounds write flaw in Apple's PDF processing libraries that affects multiple operating systems including iOS, iPadOS, and macOS. This type of vulnerability occurs when an application writes data beyond the boundaries of allocated memory regions, potentially allowing attackers to overwrite adjacent memory locations. The flaw specifically manifests during the processing of maliciously crafted PDF files, making it particularly dangerous in environments where PDF handling is common. The issue is classified under CWE-787, which defines out-of-bounds write vulnerabilities as a fundamental memory safety problem that can lead to arbitrary code execution when exploited successfully.
The technical exploitation of this vulnerability requires an attacker to craft a specially designed PDF document that triggers the out-of-bounds write condition within Apple's PDF rendering engine. When a user opens such a malicious PDF file, the vulnerable code path executes and allows the attacker to write data beyond the intended memory boundaries. This memory corruption can be leveraged to overwrite critical program variables, function pointers, or return addresses, ultimately enabling the execution of arbitrary code with the privileges of the affected application. The vulnerability affects the core PDF processing functionality that is utilized across various Apple applications including Safari, Preview, and other document viewing components, making it a widespread concern across the Apple ecosystem.
From an operational perspective, this vulnerability poses significant risks to enterprise and individual users who regularly interact with PDF documents. The attack vector is particularly concerning because PDF files are commonly shared through email, cloud storage services, and web downloads, providing multiple entry points for exploitation. The arbitrary code execution capability means that successful exploitation could lead to complete system compromise, data theft, or deployment of additional malware. Organizations relying on Apple devices for business operations face potential security breaches that could result in intellectual property theft, financial loss, or regulatory compliance violations. The vulnerability's impact is amplified by the fact that it affects multiple platforms simultaneously, requiring coordinated patch management across various device types and operating system versions.
Apple addressed this vulnerability by implementing improved input validation mechanisms within their PDF processing libraries, specifically targeting the bounds checking procedures that were previously insufficient to prevent the out-of-bounds write condition. The fix is included in iOS 14.2, iPadOS 14.2, and macOS Big Sur 11.0.1 releases, which introduced enhanced memory validation routines and stricter bounds checking for PDF parsing operations. Security professionals should prioritize deployment of these updates across all affected systems, particularly in enterprise environments where multiple Apple devices are in use. The mitigation strategy should also include user education about avoiding suspicious PDF files and implementing additional security controls such as sandboxing and content filtering solutions to reduce the attack surface. This vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter, as successful exploitation could enable attackers to execute arbitrary commands on compromised systems, and T1566 for phishing attacks, since the initial compromise often occurs through malicious email attachments or web downloads containing crafted PDF files.